TTCN-3(Testing & Test Control Notation Version 3) is the international standard testing language defined by ETSI in 2001. TTCN-3 is generally used for protocol conformance test, but it is also possible to be applied to the platform and API tests based on CORBA. Moreover, it can be also applied to the various testings such as interworking testing, repetition testing, platform testing, etc. IEC 61850 is the protocol proposed for SAS(Substation Automation System) of SCADA(Supervisory Control And Data Acquisition) system. In this paper, a IEC 61850 interoperability Tester based TTCN-3 is developed under the Window environment. IEC 61850 Server Simulator of Linux operating system is used as SUT(System Under Test). Conformance testing items in this paper are the Positive test case_Srv5 of "Server, Logical device, Logical node, and data model" in the testing group of "IEC 61850 - Part10" document.